Numerical analysis method for rock mass engineering based on IMASS constitutive model

Abstract

The application relates to the technical field of geotechnical engineering, and particularly discloses a rock mass engineering numerical analysis method based on an IMASS constitutive model, which comprises the following steps: according to the geometric size of a slope or a tunnel and the physical and mechanical properties of a rock mass, a three-dimensional numerical model is established in numerical simulation software, and the parameters of the rock mass are determined; the IMASS constitutive model is called in the numerical simulation software, and the parameters of the IMASS constitutive model are set; numerical simulation calculation is carried out in the numerical simulation software, stress, displacement and plastic zone distribution of the rock mass in the excavation process are analyzed, and the strain softening characteristics of the IMASS constitutive model are utilized to capture the transition process of the rock mass from the peak strength to the residual strength. The rock mass engineering numerical analysis method based on the IMASS constitutive model can effectively simulate the whole process of the rock mass from being complete to being broken and then expanding, and has a significant advantage in dealing with the complex behaviors such as strain softening and expansion of the rock mass, so that the accuracy and reliability of the tunnel stability analysis are improved.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a numerical analysis method for rock mass engineering based on the IMASS constitutive model. Background Technology

[0002] In large-scale geotechnical engineering, stability analysis of slopes and tunnels is a crucial step in ensuring project safety. Traditional numerical analysis methods, such as the Mohr-Coulomb criterion and the Drucker-Prager criterion, have limitations in handling complex behaviors of rock masses, such as strain softening and expansion. These traditional models often fail to adequately consider the strength reduction and volume expansion of rock masses due to damage and fracturing during excavation, making it difficult to accurately simulate the actual mechanical response of the rock mass during excavation. For example, the Mohr-Coulomb criterion does not consider the influence of intermediate principal stresses on rock strength, while the Drucker-Prager criterion, although considering intermediate principal stresses, still falls short in simulating the strain softening behavior of rock masses.

[0003] The IMASS constitutive model, as an emerging strain softening model, can effectively describe the entire process of rock mass from intact to fractured and then to expansion. Based on the empirical Hoek-Brown criterion, it uses strain and element-related properties to reflect the influence of volumetric changes during plastic deformation of the rock mass. The IMASS constitutive model includes two softening (or residual) yield envelopes to represent the two-stage softening behavior of the rock mass, distinguishing between damage (caused by fracture and associated loss of cohesion and tensile strength) and subsequent disturbance (due to volumetric expansion). This two-stage softening / weakening characteristic is crucial for accurately characterizing the post-peak behavior of rock masses in underground excavation and open-pit mining applications.

[0004] However, there is currently a lack of systematic methods and parameter optimization strategies for applying the IMASS constitutive model to numerical simulation analysis of tunnels. How to fully leverage the advantages of the IMASS constitutive model and improve the accuracy and reliability of tunnel stability analysis has become an urgent problem to be solved. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems mentioned above, and to provide a numerical analysis method for rock mass engineering based on the IMASS constitutive model, so as to improve the accuracy and reliability of tunnel stability analysis.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a numerical analysis method for rock mass engineering based on the IMASS constitutive model, comprising the following steps:

[0007] Model establishment and parameter determination: Based on the geometric dimensions of the slope or tunnel and the physical and mechanical properties of the rock mass, a three-dimensional numerical model is established in the numerical simulation software, and the density of the rock mass, the GSI value in the Hoek-Brown criterion, the uniaxial compressive strength UCS, the material constant mi, and the original rock modulus parameter are determined.

[0008] IMASS constitutive model calling and parameter setting: Call the IMASS constitutive model in the numerical simulation software and set the parameters of the IMASS constitutive model;

[0009] Numerical analysis and result processing: Numerical simulation calculations are performed in numerical simulation software to analyze the stress, displacement, and plastic zone distribution of the rock mass during the excavation process. The strain softening characteristics of the IMASS constitutive model are used to capture the transformation process of the rock mass from peak strength to residual strength.

[0010] Preferably, the establishment of the three-dimensional numerical model includes the following steps:

[0011] Importing the geometric model: Use the zone import command to import a pre-generated mesh file, defining the geometry and mesh generation of the slope or tunnel;

[0012] Define zone groups: Use the zone group command to mark different zones in the model to distinguish between the rock mass and the excavation area;

[0013] Generate outer surface mesh: Use the zone face skin command to generate the outer surface mesh of the model.

[0014] Preferably, the invocation and parameter setting of the IMASS constitutive model include:

[0015] a) Invoking the IMASS constitutive model: Use the commands `model configure imass` and `zone cmodel assignimass` to configure the model and specify that the IMASS constitutive model should be used;

[0016] b) Set IMASS model parameters: Assign the rock mass physical and mechanical parameters to the unit cells one by one using the zone property command, and activate IMASS’s unique peak-residual-limit three-stage strength evolution and volume expansion algorithm. The rock mass physical and mechanical parameters include intact modulus, geological strength index GSI, material constant mi, uniaxial compressive strength UCS, and weakening multi-criteria coefficient.

[0017] Preferably, the numerical simulation calculation includes the following steps:

[0018] Apply boundary conditions: Use the zone face apply command to apply boundary conditions and fix the velocity of the model in each direction;

[0019] Initialize in-situ stress: Define tunnel depth, maximum z-coordinate and gravitational acceleration, apply gravity, and initialize the initial stress of the rock mass;

[0020] Reset displacement, velocity, and state: Use the zone gridpoint initialize and zone initializestate commands to set the initial displacement, velocity, and state of all grid points to zero;

[0021] Define FISH functions: Write functions using the FISH language to calculate and record axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus parameters;

[0022] Excavation relaxation: Use the zone relax excavate command to define the excavation area and set the excavation parameters to simulate the step-by-step excavation process of the tunnel;

[0023] Solve the model: Solve the model using the model solve command to simulate the mechanical response of the rock mass during the excavation process;

[0024] Save model state: Use the model save command to save the model's calculation results and state to a file.

[0025] Preferably, the IMASS constitutive model includes a rock mass strength peak envelope and two softening yield envelopes. The definition formula for the rock mass strength peak envelope is:

[0026] ,

[0027] ,

[0028] ,

[0029] ;

[0030] The defining formulas for the two softening yield envelopes are:

[0031] ,

[0032] in, It is shear strength. It is normal stress. Equivalent roughness, It is the strength of the rock block, and It is the basic angle of friction of the rock block;

[0033] ,

[0034] It's porosity. It is the rounding exponent, where For partially rounded / smooth blocks, For angular / rough blocks, and Applicable to very sharp, angular / very rough blocks, when shear strength is converted into a strength envelope. The space is approximated by the Hoek-Brown envelope with the following parameters:

[0035] ,

[0036] ,

[0037] ,

[0038] Maximum porosity is 40%. The default value is 30°.

[0039] Preferably, the calculation formulas for the parameters such as axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus are as follows:

[0040] Axial strain :

[0041] ,

[0042] in, To monitor the displacement of the point in the Z direction, () represents the initial height of the sample or rock mass;

[0043] Damage indicators :

[0044] ,

[0045] in, This is the first principal stress; It is the third principal stress; It is the peak first principal stress; Alternatively, it can be directly defined by internal state variables of IMASS, characterizing the degree of softening from peak intensity to residual intensity, with a value range of [value range missing]. ;

[0046] Volumetric strain increment :

[0047] ,

[0048] in, For the strain increments in each principal direction;

[0049] Cohesion With friction angle :

[0050] Based on the generalized Hoek-Brown strength criterion and damage state evolution:

[0051] ,

[0052] in, , , ,

[0053] Cohesion With friction angle The equivalent of obtaining the tangents of the Mohr-Coulomb envelope and the Hoek-Brown envelope under the current stress state is as follows:

[0054] ,

[0055] ,

[0056] density :

[0057] When considering the volume expansion effect, the density is updated as a function of porosity:

[0058] ,

[0059] in, For the initial density, and These are the initial volume and the current volume, respectively.

[0060] Tangent modulus :

[0061] Based on geological intensity indicators by the IMASS model intact rock modulus and damage status evolution:

[0062] ,

[0063] Among them, the degenerate function It can be represented as:

[0064] , ( Take 10~15).

[0065] Compared with existing technologies, the numerical analysis method for rock mass engineering based on the IMASS constitutive model of the present invention has the following advantages:

[0066] (1) The IMASS constitutive model can better describe the entire process of rock mass from integrity to fragmentation and then to expansion. It has significant advantages in simulating complex behaviors such as strain softening and expansion of rock mass. It can more realistically reflect the mechanical behavior of rock mass during excavation and improve the accuracy of tunnel stability analysis.

[0067] (2) By accurately simulating the mechanical behavior of rock mass during excavation, a more reliable basis can be provided for support design, thereby reducing engineering risks and costs and optimizing the support design and construction process of tunnels.

[0068] (3) Applying the IMASS model to the numerical analysis of tunnels provides a new tool for numerical analysis of geotechnical engineering, expands the application scope of the IMASS constitutive model, and has broad application prospects. Attached Figure Description

[0069] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0070] Figure 1 This is a schematic diagram of the three envelope curves of the IMASS constitutive model;

[0071] Figure 2 This is a schematic diagram of the rock mass response to stress-strain behavior in the IMASS constitutive model.

[0072] Figure 3 This is a schematic diagram illustrating the loss caused by different degrees of damage and disturbance in a rock mass using the IMASS constitutive model.

[0073] Figure 4 This is a flowchart of stability analysis for different geotechnical engineering projects using the IMASS constitutive model;

[0074] Figure 5 This is a graph showing the displacement variation of a specimen in a uniaxial unconfined compression test.

[0075] Figure 6 This is a diagram showing the stress variation of a specimen in a uniaxial unconfined compression test.

[0076] Figure 7 The stress-strain response curve of the specimen in the uniaxial unconfined compression test.

[0077] Figure 8 The graph shows the variation of different rock mass parameters of the uniaxial unconfined compression test specimens with the excavation process.

[0078] Figure 9 The stress-strain variation curves for stability analysis of the support column;

[0079] Figure 10 The displacement variation diagram is for the stability analysis of the support column;

[0080] Figure 11 This is a graph showing the variation of the minimum principal stress (most compressible) in the stability analysis of the support column;

[0081] Figure 12 The graph shows the maximum shear strain variation in the support stability analysis.

[0082] Figure 13 A graph showing the variation of the sloss index in the IMASS constitutive model for pillar stability analysis;

[0083] Figure 14 This is a diagram showing the vertical displacement of the arch crown.

[0084] Figure 15 This is a diagram showing the horizontal displacement of the arch crown. Detailed Implementation

[0085] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0086] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a central component. When a component is described as "connected to" another component, it can be directly connected to the other component or may have a central component. When a component is described as "set on" another component, it can be directly set on the other component or may have a central component. When a component is described as "set in the middle," it is not simply set in the exact center, as long as it is not set within the area defined by both ends being in the middle. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0087] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0088] This application discloses a numerical analysis method for rock mass engineering based on the IMASS constitutive model, including the following steps:

[0089] Step 1, Model Building and Parameter Determination:

[0090] First, a three-dimensional numerical model is established in numerical simulation software based on the geometric dimensions of the tunnel and the physical and mechanical properties of the rock mass. In order to model the strain burst-related mechanism, certain properties need to be considered numerically, including the following four properties: (1) three-dimensional (3D) model meshing to illustrate the 3D stress state in XYZ space; (2) fine meshing of the expected dynamic behavior region (tunnel rock mass, tunnel rock mass boundary rock mass boundary), which explains the non-uniformity, capture of tangential stress changes and the existence of transverse discontinuities; (3) initial stress state is initialized by displacement boundary conditions to take into account the rock mass loading history; (4) selection of constitutive models that consider failure and replicate rock mass yielding.

[0091] Taking FLAC3D as an example, this is a numerical simulation software widely used in geotechnical engineering. The following is an explanation of the modeling process, model features, formula representation, and input / output for slopes and tunnels:

[0092] Model Feature Construction: A 3D model is built based on the actual geometric dimensions of the slope and tunnel. For example, the slope angle, height, and width, and the tunnel diameter, length, and location must all be accurately input. A 3D meshing technique is used to divide the model into multiple elements to reflect the 3D stress state in XYZ space. Fine meshing is applied to the expected dynamic behavior areas, such as the tunnel rock mass and its boundaries, to capture inhomogeneities, tangential stress variations, and discontinuities across the surrounding rock. The initial stress state is initialized using displacement boundary conditions, considering the loading history of the rock mass. A suitable constitutive model is selected to consider the failure and yielding of the rock mass. For example, the IMASS constitutive model can be used to describe the plastic yielding and stress softening of soil and rock materials. The model input parameters include: geometric parameters, such as the dimensions of the slope and tunnel; material parameters, such as Young's modulus, Poisson's ratio, cohesion, and internal friction angle of the rock mass; and boundary conditions, such as displacement boundary conditions and stress boundary conditions. The model's output metrics include: stress distribution, such as von Mises stress cloud diagrams; displacement distribution, which reflects the deformation of the rock mass; and failure zones, which can be calculated using the IMASS constitutive model.

[0093] The specific applications of the above four attributes in modeling are as follows:

[0094] 1) 3D Model Meshing: In FLAC3D, the model is divided into a 3D mesh using the mesh generation function. The mesh type can be selected as tetrahedral or hexahedral to accommodate different geometries and accuracy requirements. By controlling the mesh density, it is ensured that the model accurately reflects the 3D stress state.

[0095] 2) Fine mesh refinement in areas of anticipated dynamic behavior: Local mesh refinement is performed in key areas such as the tunnel rock mass and its boundaries. For example, FLAC3D's local mesh refinement function can be used to improve the ability to capture inhomogeneities and stress changes.

[0096] 3) Initial stress state initialization: Based on the loading history of the rock mass, set displacement boundary conditions. Calculate the initial stress field and use it as the initial state of the model.

[0097] 4) Selection of Constitutive Model: Based on the mechanical properties of the rock mass, select a suitable constitutive model. For example, the Mohr-Coulomb model can be used to describe the yielding of soil and rock materials. In FLAC3D, the constitutive model is applied to the model by defining material properties.

[0098] For different types of rock masses, determine their density, GSI value in the Hoek-Brown criterion, uniaxial compressive strength (UCS), and material constants respectively. Parameters such as the original rock modulus are crucial for improving the accuracy of numerical analysis. Determining the parameters of the IMASS model is key to improving the accuracy of numerical analysis and requires reasonable selection based on the actual physical and mechanical properties of the rock mass.

[0099] The specific method for determining the above parameters is as follows:

[0100] Density: Measured through laboratory testing or field sampling. In numerical models, density is used to calculate the self-weight and inertial forces of the rock mass and is an important parameter for determining the stress field.

[0101] GSI (Geological Strength Index): It can be determined by looking up a table based on the degree of joint development and rock block integrity of the rock mass, or by calculating it through RMR or Q value (for RMR>23, GSI=RMR-5; for RMR<23, GSI=9logQ+44).

[0102] RMR (Rock Mass Quality Rating System) was proposed by Bieniawski in 1973 to quantitatively evaluate the engineering properties of rock masses. Its core is to score through 6 indicators, with a total score range of 0–100 points.

[0103] RMR scoring indicators and weights

[0104]

[0105] GSI (Geological Strength Index) is used in the Hoek-Brown criterion to characterize the structural features of rock masses, and its range is typically 10–90. The conversion relationship between RMR and GSI is as follows:

[0106] 1. Standard conversion formula

[0107] When RMR ≥ 23:

[0108] GSI=RMR89−5

[0109] Note: RMR89 refers to the 1989 version (including joint condition adjustment).

[0110] When RMR < 23:

[0111] GSI=9⋅lnQ+44

[0112] Where Q is the rock mass quality index (Barton, 1974), which needs to be calculated using the following formula:

[0113] ,

[0114] Rock quality index (%)

[0115] : Number of joint groups (1–20)

[0116] Joint roughness (0.5–4).

[0117] : Joint alteration degree (0.75–20)

[0118] Groundwater influence coefficient (0.05–1).

[0119] Stress reduction factor (0.5–400).

[0120] Uniaxial compressive strength (UCS): Obtained through uniaxial compression tests. UCS is an important indicator of rock mass strength and is used to calculate the peak strength of the rock mass.

[0121] Material constants ( ): It is usually approximately determined by the ratio of the uniaxial compressive strength to the tensile strength of intact rock. The parameters used to calculate the strength of rock masses are key parameters in the Hoek-Brown criterion.

[0122] Intact Rock Modulus: Obtained through uniaxial compression tests or elastic modulus tests. The intact rock modulus describes the elastic behavior of rock masses and is an important parameter for calculating stress-strain relationships.

[0123] Model input instructions

[0124] Density: Entered via the zone initialize density command.

[0125] GSI value: Entered via the zone property in_stren_gsi command.

[0126] UCS value: Entered via the zone property in_stren_ucsi command.

[0127] Value: Entered via the zone property in_stren_mi command.

[0128] Original rock modulus: Entered via the command `zone property in_mod_youngintact`.

[0129] Step 2: IMASS model call, parameter setting, and GSI application.

[0130] IMASS stands for Itasca Constitutive Model for Advanced Strain Softening (IMASS). It is an advanced strain softening model used to represent the response of rock mass to stress changes caused by excavation. IMASS represents the degree of damage to slopes, caving, pillars, open spaces, and other excavated surrounding rock by continuously calculating the asymptotic failure and disintegration of the rock mass from intact, jointed, and / or vein-like rock to discrete, blocky material. Based on the empirical Hoek-Brown criterion, IMASS uses strain and element-related properties to reflect the influence of volumetric changes during plastic deformation of the rock mass. Building upon the previously developed CaveHoek constitutive model, IMASS can accurately simulate the rock mass behavior under complex stress paths, particularly the behavior of brittle rock. IMASS is currently primarily used for mining process studies in caving mining methods.

[0131] In numerical simulation software, the IMASS constitutive model is called and configured using the command `model config imasszonecmodel imass`.

[0132] The IMASS model incorporates a peak strength envelope for the Hoek-Brown rock mass and two softening (residual) yield envelopes, as shown in the attached figure. Figure 1 As shown.

[0133] Two softening (or residual) yield envelopes represent the two-stage softening behavior of rock mass, distinguishing between damage (caused by fracture and associated loss of cohesion and tensile strength) and subsequent disturbance (due to volume expansion) within the rock mass. This two-stage softening / weakening characteristic in IMASS is crucial for accurately characterizing the post-peak behavior of rock mass in underground excavation and open-pit mining applications.

[0134] The peak intensity envelope (red curve) is defined by the generalized Hoek-Brown criterion:

[0135] ,

[0136] ,

[0137] ,

[0138] ,

[0139] Two residual envelopes describe the behavior of cohesive, perfectly frictional materials with varying degrees of interlocking. The first residual envelope represents the post-peak strength of the rock. At this point, it is assumed that the rock mass has fractured, but the resulting rock fragments are still perfectly interlocked, with zero porosity. The second residual envelope represents the ultimate residual strength of the rock mass. At this point, the degree of interlocking of the rock fragments is minimal, and the porosity is maximum (up to 40%).

[0140] Ideally, the first and second residual envelopes describe the behavior of cohesive, perfectly frictional materials with different degrees of interlocking.

[0141] ,

[0142] It is shear strength. It is normal stress. Equivalent roughness, It is the strength of the rock block, and It is the basic angle of friction of the rock.

[0143] ,

[0144] It's porosity. It is the rounding exponent, where For partially rounded / smooth blocks, For angular / rough blocks, and Suitable for very sharp, angular / very rough blocks. When converting shear strength to strength envelope. The space can be approximated by the Hoek-Brown envelope with the following parameters:

[0145] ,

[0146] ,

[0147] ,

[0148] Maximum porosity, i.e., 40%. Default is 30°.

[0149] Based on the characteristics of the rock mass, the parameters of the IMASS model, including the critical plastic shear strain coefficient, should be set appropriately. The parameter settings of the IMASS model can fully reflect the strain softening behavior of the rock mass during excavation and capture the transformation process of the rock mass from peak strength to residual strength.

[0150] When yielding occurs, the instantaneous cohesion decreases linearly from its peak to post-peak (zero cohesion in unconfined rock) and accumulates plastic shear strain. The critical shear strain is defined as the total plastic shear strain required to reduce the cohesion of the rock mass from its peak to zero. At this point, the rock mass is at post-peak strength. The smaller the critical plastic strain, the more brittle the rock mass.

[0151] Higher quality rock masses (higher GSI) and larger solid rock volumes involved in the failure process typically function in a more brittle manner, thus exhibiting lower critical strain values. Conversely, lower quality rock masses (lower GSI) with higher fracture frequencies typically function in a more ductile manner, thus exhibiting higher critical strain values.

[0152] Estimates of the relationship between critical strain and GSI were determined by retrospective analysis of rock mass failure in caves and other openings. These estimates provide a starting point for describing the degree of strain softening used in collapse simulations.

[0153]

[0154] Area size (in meters).

[0155] The region size present in this relationship indicates that the critical strain parameter is related to the region size in the continuum model, where shear tends to be analytical in a band approximately one region thick. By default, in IMASS, the critical plastic shear strain for each region is calculated and stored using the region size according to equation (10). A multiplier It can be applied to calculate region-based critical plastic shear strain to refine the region brittleness.

[0156] Between the post-peak envelope and the ultimate strength envelope, the frictional properties of the rock mass are controlled by its volumetric strain increment (VSI) rather than plastic shear strain. This demonstrates the dependence of rockfill shear strength on porosity. Because the VSI in the region does not increase monotonically (unlike plastic shear strain), the rock mass strength envelope weakens or strengthens between the post-peak and ultimate strength envelopes as porosity changes. This is a powerful feature that allows for the capture of rock mass strength increases gained due to recompaction.

[0157] Appendix Figure 2 The rock mass response to stress-strain behavior in IMASS is shown, and it summarizes the scales for rock mass softening / weakening between peak and post-peak and between post-peak and ultimate strength envelopes.

[0158] Sloss—a damage indicator in IMASS.

[0159] Sloss is a damage index in IMASS and can be used to assess the degree of softening / weakening experienced by the rock mass. Sloss varies between [-1, 1].

[0160] Between the peak intensity and post-peak intensity envelopes:

[0161] ,

[0162] Between the peak intensity and the limiting intensity envelope:

[0163] ,

[0164] Appendix Figure 3 The diagram schematically illustrates the loss of rock mass due to varying degrees of damage and disturbance. At point "C," it is assumed that the rock mass has fractured, but the resulting rock fragments remain completely interlocked (cohesion within the rock mass is completely lost, but friction is high). At this point, the stress exceeds the rock's spalling or fracture strength. However, experience shows that underground openings are stable with minimal support. At point "D," the degree of rock fragment interlocking is minimal, and porosity is maximized. Under this stress state, unlined shafts or minimally supported tunnels are considered unusable. If calibrated according to the damage condition of the sloss, it can be a powerful tool for predicting the suitability and stability of structures.

[0165] Step 3: Numerical analysis and result processing.

[0166] The specific steps in numerical simulation software (such as FLAC3D) are as follows:

[0167] 3.1 Model Initialization

[0168] Large deformation switch: Set `large-strain on` in the `config dyn` command to activate the large deformation algorithm in finite strain mode.

[0169] Model naming: Create a new computational domain named "Stability Analysis" using model new.

[0170] Constitutive model import: Execute `model configure imass` to load the IMASS kernel dynamic link library.

[0171] 3.2 Geometric Modeling

[0172] Regional group division:

[0173] Surrounding rock area: Use zone create brick to build a cuboid containing the excavation body (size based on on-site survey data).

[0174] Excavation area: Define the group of units to be dynamically removed (geometry matching the tunnel design cross section) using group excavate.

[0175] Mesh generation: The outer surface is triangulated using zone generate-from-surfaces, and the maximum element size is set to ≤1 / 10 of the tunnel span.

[0176] 3.3 Model Attribute Definition

[0177]

[0178] 3.4 Boundary Condition Setting

[0179] Velocity constraint: Apply `zone face apply velocity-normal 0` to the bottom and surrounding surfaces of the model to simulate infinite boundary conditions.

[0180] Stress boundary: Equivalent overlying strata pressure σ_v=γ is applied at the top. h (γ is the unit weight of the rock mass, h is the burial depth).

[0181] 3.5 Initialization of geostress

[0182] A phased balancing method is adopted:

[0183] The model solves elasticity pre-calculation.

[0184] Zone initializes stresses overburden by applying a self-weight stress field.

[0185] The model cycle is 5000 iterations until the force residual is <1e-5.

[0186] 3.6 State Reset

[0187] Executing the zone gridpoint reset displacement will reset the displacement to zero.

[0188] `zone initialize velocity 0` clears the node velocity field.

[0189] Set the zone property state to 0 to reset the rock mass damage state variable.

[0190] 3.7 FISH Function Development

[0191] Using functions written in the FISH language, calculate and record axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus parameters. The total displacement calculation of the FISH function is as follows:

[0192] define total_disp

[0193] sum_dx = 0

[0194] sum_dy = 0

[0195] loop foreach gp gp.list

[0196] sum_dx = sum_dx + gp.disp.x(gp)

[0197] sum_dy = sum_dy + gp.disp.y(gp)

[0198] end_loop

[0199] total_disp_x = sum_dx / gp.num

[0200] total_disp_y = sum_dy / gp.num

[0201] end

[0202] Real-time monitoring: During the solution process, call `history add fish total_disp_x` to record the evolution curve.

[0203] The calculation formulas for parameters such as axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus are as follows:

[0204] Axial strain :

[0205] ,

[0206] in, To monitor the displacement of the point in the Z direction, () represents the initial height of the sample or rock mass;

[0207] Damage indicators :

[0208] ,

[0209] in, This is the first principal stress; It is the third principal stress; It is the peak first principal stress; Alternatively, it can be directly defined by internal state variables of IMASS, characterizing the degree of softening from peak intensity to residual intensity, with a value range of [value range missing]. ;

[0210] Volumetric strain increment :

[0211] ,

[0212] in, For the strain increments in each principal direction;

[0213] Cohesion With friction angle :

[0214] Based on the generalized Hoek-Brown strength criterion and damage state evolution:

[0215] ,

[0216] in, , , ,

[0217] Cohesion With friction angle The equivalent of obtaining the tangents of the Mohr-Coulomb envelope and the Hoek-Brown envelope under the current stress state is as follows:

[0218]

[0219] ,

[0220] density :

[0221] When considering the volume expansion effect, the density is updated as a function of porosity:

[0222] ,

[0223] in, For the initial density, and These are the initial volume and the current volume, respectively.

[0224] Tangent modulus :

[0225] Based on geological intensity indicators by the IMASS model intact rock modulus and damage status evolution:

[0226] ,

[0227] Among them, the degenerate function It can be represented as:

[0228] , ( Take 10~15).

[0229] 3.8 Excavation and relaxation

[0230] The stress relief method is adopted: the stress in the excavation zone is relieved in N steps (usually N=3) proportionally.

[0231] Zone relax excavate 1 stress 0.33 # First step to release 33% of the stress.

[0232] Model step 1000,

[0233] Zone relax excavate 1 stress 0.67 # Step 2 cumulatively releases 67%

[0234] Model step 1000,

[0235] zone relax excavate 1 stress 1.0 # Completely relieve stress.

[0236] 3.9 Solving for control

[0237] Invoking the implicit solver: model solves imass-convergence.

[0238] Convergence criteria: Simultaneously satisfying the force residual ratio <0.01% and the maximum displacement change rate <1e-6 m / step.

[0239] 3.10 Result Output

[0240] Save the complete model state: `model save 'FinalState.sav' binary archive`

[0241] Export key data: plastic strain contour map, damage index distribution, displacement vector field, etc.

[0242] The above numerical analysis and result processing steps can be summarized as follows: Initialize the model (whether to enable the large deformation switch, import the IMASS constitutive model, name the model as stability analysis), import the geometric model, define the region group (surrounding rock region and excavation region), define the model properties (assign material IMASS constitutive properties, rock density, rock modulus, rock GSI, rock...). The steps include: defining rock UCSI and rock softening release coefficient; defining boundary conditions (setting boundary velocities to 0 in all directions); initializing geostress; resetting displacement velocities and states; defining the fish function (calculating total horizontal and vertical displacements); starting relaxation excavation; solving the model until convergence; and saving the model. Internal operations of the numerical simulation software can be found in the appendix. Figure 4 .

[0243] Numerical simulations were performed to analyze the stress, displacement, and plastic zone distribution of the rock mass during tunnel excavation. Utilizing the strain softening characteristics of the IMASS model, complex behaviors such as rock mass fracturing and expansion during excavation were accurately simulated. By comparing numerical results under different excavation schemes, the tunnel support design and construction technology were optimized. The application of the IMASS model makes the numerical analysis results more consistent with the mechanical behavior of the rock mass during actual excavation, improving the reliability of tunnel stability analysis.

[0244] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0245] Example 1: Uniaxial unconfined compression test using the IMASS constitutive model, such as... Figures 5 to 8 As shown, the specific method is as follows:

[0246] S101 Model Initialization and Configuration: Start the numerical simulation software program and create a new model instance; disable the large strain option by using the command `model large-strain off`, which is suitable for simulating the mechanical behavior of soil and rock materials under small strain conditions, ensuring calculation accuracy and stability; configure the model using the command `model configure imass`, specifying the use of the IMASS constitutive model, which can effectively simulate the complex mechanical properties of rock mass such as strain softening and expansion during loading.

[0247] S102 Global Variable Definitions: A global variable `cofStress` is defined using `[global cofStress = 0.0]` to apply initial stress. Its value is set to 0.0, indicating an initial stress-free state. A global variable `appliedVelocity` is defined using `[global appliedVelocity = 1.e-6]` to control the applied vertical velocity during loading. Its value is set to 1.e-6 to ensure that the loading process is slow and controllable.

[0248] S103 Geometric Model Construction: Using the command "zone create brick size 1 1 1", a cubic unit with a size of 1m×1m×1m is created as the simulation object of the experiment. This unit represents the soil and rock material sample to be tested.

[0249] S104 Material Property Assignment: The IMASS constitutive model is assigned to all elements using the zone cmodel assign imass command, enabling it to simulate the mechanical behavior of soil and rock materials; the stress state of the elements is initialized using the zone initialize stress xx[cofStress] yy [cofStress] zz [cofStress] command based on the previously defined cofStress value, ensuring that the model is in a stress-free state at the initial moment.

[0250] S105 sets the density and configures the IMASS model parameters: Using the command `zone initialize density 2600`, assign a density value of 2600 kg / m³ to the element. This density value needs to be adjusted according to the actual density of the soil and rock materials. Set the geological strength index (GSI) of the rock mass to 70.0; this parameter reflects the integrity of the rock mass. Set the uniaxial compressive strength of the rock mass to 100.0 MPa, i.e., 100.0e6 Pa. Specify the material constant mi as 15.0; this parameter is related to the frictional characteristics of the rock mass. Set the integrity modulus of the rock mass to 40 GPa, i.e., 40e9 Pa, reflecting the elastic modulus of the rock mass before damage occurs. Define the weakening multi-criteria coefficient as 0.25 to control the degree of strength reduction of the rock mass during the softening process. Enable the volume expansion density adjustment flag so that the model can simulate the density change of the rock mass due to volume expansion during loading.

[0251] S106 Boundary Condition Application: The initial velocity of all grid points is set to zero using the command `zone gridpoint initialize velocity (0,0,0)`, ensuring that the model is stationary at the initial moment; the vertical velocity of the bottom grid points is fixed using the command `zone gridpoint fix velocity-z range position-z 0.0`, simulating the constraint conditions at the bottom in the actual experiment.

[0252] S107 Stress boundary condition application: Apply horizontal stress to the left side of the model, with the stress value determined by cofStress, to simulate the left boundary condition; apply horizontal stress to the right side of the model, with the stress value also determined by cofStress, to simulate the right boundary condition; apply vertical stress to the top of the model, with the stress value determined by cofStress, to simulate the top boundary condition.

[0253] S108 Historical Data Recording: Create a global pointer gpPtr, pointing to the grid point near (1,1,1) in the model, for subsequent data acquisition; create a global pointer znPtr, pointing to the first cell in the model, for subsequent data acquisition.

[0254] S109 FISH Function Writing: The function `axialStrain`, written in the FISH language, is used to calculate and record parameters such as axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus. The function retrieves relevant data and performs calculations by accessing the grid points and element properties pointed to by the global pointer.

[0255] Calculate axial strain as a percentage; obtain the damage index sloss; obtain the volumetric strain increment vsi; obtain the cohesion coh; obtain the friction angle fric; obtain the density dens; obtain the modulus modulus; obtain the maximum principal stress s1; obtain the minimum principal stress s3.

[0256] S110 calls the FISH function: The FISH function axialStrain is called through the [axialStrain] command, so that it is executed periodically during the model operation to record relevant data.

[0257] S111 Loading and Solving: Using the command `zone face apply velocity-z [-appliedVelocity]range position-z 1.0`, a vertical velocity is applied to the top of the model. The velocity value is `-appliedVelocity`, and the negative sign indicates that it is applied downwards, simulating the loading process in a uniaxial unconfined compression test.

[0258] S112 Records Historical Data: Utilizing FLAC3D's built-in history function, it records the maximum mechanical unbalanced value of the model during the loading process (model history mechanical unbalanced-maximum), as well as data such as axial strain, damage index, volumetric strain increment, cohesion, friction angle, maximum principal stress, minimum principal stress, density, and modulus recorded through the FISH function (fish history command).

[0259] S113 Model Cyclic Solution: The model is used to perform 100,000 calculation cycles by using the command "model cycle 100000" to simulate the mechanical response process of soil and rock materials in a uniaxial unconfined compression test.

[0260] S114 Save Model State: Finally, use the command `model save 'UnconfinedCompression.sav'` to save the model's calculation results and state as the file `UnconfinedCompression.sav` for easy analysis and review later.

[0261] Example 2: Stability analysis of the support pillar using the IMASS constitutive model, such as... Figures 9 to 13 As shown, the specific method is as follows:

[0262] S201 Model Initialization and Configuration: Start the numerical simulation software program and create a new model instance to lay the foundation for subsequent numerical simulations; disable the large strain option by using the command `model large-strain off`, which is suitable for simulating the mechanical behavior of soil and rock materials under small strain conditions, ensuring calculation accuracy and stability; configure the model using the command `model configure imass`, specifying the use of the IMASS constitutive model, which can effectively simulate the complex mechanical properties of rock mass such as strain softening and expansion during loading.

[0263] S202 Geometric Model Construction: The geometric parameters of the model are defined using the FISH function `geometry`, including column height (hp), room width (wr), column width-to-height ratio (wh_ratio), and element size (z_size). Based on these parameters, derived parameters such as column width (wp), half-width (half_wp), room half-width (half_wr), total half-width (half_w), support height (roof_height), and support top position (roof_top) are calculated. The geometric model is created through methods such as creating geometry, reflection symmetry, and mesh generation.

[0264] Create geometry: Use the `zone create brick` command to create a brick unit with dimensions [-half_w] 0 0 to 0 00, [-half_w] [z_size] 0 to [-half_w] 0 [roof_height], representing the main body of the rock mass. The unit is divided into xel_side x-direction elements, 1 y-direction element, and zel_side z-direction elements, belonging to the group 'rock'. Define the support region: Use the `zone group 'room'` command to mark the region located between [-half_w] [-half_wp] and 0 0, with the z-direction from 0 to half_hp, as 'room'. Create the top geometry: Use the `zone create brick` command to create a unit with dimensions [-half_w] 0 [roof_height] to 0 0 [roof_height], [-half_w] [z_size] [roof_height] to [-half_w] 0. The [roof_top] brick unit represents the top structure. The unit is divided into xel_side x-direction units, 1 y-direction unit, and top_zel_side z-direction units, belonging to the group 'rock'.

[0265] Reflection symmetry: Use the zone reflect command to perform reflection symmetry operations in the x and z directions to generate a complete geometric model.

[0266] Generate mesh: Use the zone face skin command to generate the outer surface mesh of the model, which is convenient for applying boundary conditions and viewing the results later.

[0267] S203 Boundary Condition Application: Use the `zone face apply velocity-x 0` command to fix the velocity in the x-direction to 0, applicable to the west ('West') and east ('East') sides of the model; use the `zone face apply velocity-y 0` command to fix the velocity in the y-direction to 0, applicable to the north ('North') and south ('South') sides of the model; use the `zone face apply velocity-z 0` command to fix the velocity in the z-direction to 0, applicable to the bottom ('bottom') and top ('top') sides of the model.

[0268] S204 Material Property Assignment: Use the `zone delete range group 'room'` command to delete the area marked 'room' to simulate actual room excavation; use the `zone cmodel assign imass` command to assign the IMASS constitutive model to all elements, enabling it to simulate the mechanical behavior of the rock mass; use the `zone initialize density2500.0` command to assign a density value of 2500 kg / m³ to the elements; Configure IMASS model parameters: Set the complete modulus of the rock mass to 30 GPa, set the geological strength index (GSI) of the rock mass to 60.0, specify the material constant mi as 15.0, set the uniaxial compressive strength of the rock mass to 50 MPa, and define the weakening multi-criteria coefficient as 1.0.

[0269] S205 Historical Data Recording: Create a global pointer gps_top, pointing to all grid points in the model belonging to the 'Top' group, for subsequent data acquisition; create a global pointer gp_top1, pointing to the grid point in the model near (0,0,roof_top), for subsequent data acquisition.

[0270] S206 defines the FISH function: the FISH function stress_top is used to calculate the sum of the unbalanced forces at the top grid points in the z direction and divide it by the area_pillar of the support column to obtain the top stress; the FISH function strain_zz is defined to calculate the z-direction displacement of the top grid points and convert it into strain values ​​(expressed as a percentage).

[0271] S207 Record Historical Data: Use the fish history stress_top command to record historical data of top stress; use the fish history strain_zz command to record historical data of strain in the z-direction.

[0272] S208 Loading and Solving: The `zone face apply velocity-z [appliedVel]` command applies a vertical velocity `appliedVel` to the bottom of the model to simulate the loading process; the `zone face apply velocity-z [-appliedVel]` command applies a vertical velocity `-appliedVel` in the opposite direction to the top of the model to simulate the reaction force at the top; the `zone mechanical damp combined` command enables combined damping to stabilize the dynamic response of the model; the `history interval 500` command sets the interval for recording historical data to 500 calculation cycles; the `modelcycle 500000` command performs 500,000 calculation cycles to simulate the mechanical response of the rock mass support under vertical loading; finally, the `model save 'pillarImass'` command saves the model's calculation results and state as the file `pillarImass` for subsequent analysis and review.

[0273] Example 3: Tunnel stability analysis using the IMASS constitutive model, such as... Figure 14 and Figure 15 As shown, the specific method is as follows:

[0274] S301 Model Initialization and Configuration: Start the numerical simulation software program and create a new model instance to lay the foundation for subsequent numerical simulations; disable the large strain option using the command `model large-strain off`, which is suitable for simulating the mechanical behavior of soil and rock materials under small strain conditions, ensuring calculation accuracy and stability; configure the model using the command `model configure imass`, specifying the use of the IMASS constitutive model, which can effectively simulate the complex mechanical properties of rock mass during loading, such as strain softening and expansion; set the model title using the command `model title 'Tunnel Stability Analysis'` for easy identification and management.

[0275] S302 Geometric Model Construction: Import the pre-generated mesh file using the `zone import 'grid.f3grid'` command. This file defines the tunnel geometry and mesh generation. Use the `zone group 'Rock'` command to label all elements as the 'Rock' group, representing the rock mass. Use the `zone group 'Excavation' range group 'Block1' slot 'Block'` command to label the excavation area as the 'Excavation' group, representing the tunnel excavation portion. Generate the outer surface mesh of the model using the `zoneface skin` command, which facilitates the application of boundary conditions and the viewing of results.

[0276] S303 Material Property Assignment: The IMASS constitutive model is assigned to all elements using the zone cmodel assign imass command, enabling it to simulate the mechanical behavior of the rock mass; the zone property density 2500 command is used to assign a density value of 2500 kg / m³ to the elements; the complete modulus of the rock mass is set to 17.4 GPa; the geological strength index (GSI) of the rock mass is set to 30.0; the material constant mi is specified as 8.0; the uniaxial compressive strength of the rock mass is set to 20 MPa; and the weakening multi-criteria coefficient is defined as 1.0.

[0277] S304 Boundary Condition Application: Use the command `zone face apply velocity-y 0.0 range group 'North' or 'South'` to fix the velocity in the y-direction to 0, applicable to the north and south sides of the model; use the command `zone face apply velocity-x 0.0 range group 'West' or 'East'` to fix the velocity in the x-direction to 0, applicable to the west and east sides of the model; use the command `zone face apply velocity-z 0.0 range group 'Bottom' or 'Top'` to fix the velocity in the z-direction to 0, applicable to the bottom and top of the model.

[0278] S305 Initial Stress Settings: Define tunnel depth as 1000.0m; define maximum z-coordinate as 35.0m; define gravitational acceleration as 9.81m / s²; apply gravity using the `model gravity [grav]` command to simulate the stress state of the rock mass under gravity; use `zone initialize-stresses overburden [-(tunnelDepth-zmax]`. grav The command `2500.0] ratio 0.5 1.0 direction-x (1,0,0)` initializes the initial stress of the rock mass, simulating the self-weight stress of the rock mass above the tunnel; the command `model solve elastic convergence 1` solves the elastic equilibrium to ensure that the model reaches equilibrium under the initial stress state.

[0279] S306 Resets Displacement, Velocity, and State: Use the zone gridpoint initialize displacement(0,0,0) command to set the initial displacement of all grid points to zero; use the zone gridpoint initialize velocity (0,0,0) command to set the initial velocity of all grid points to zero; use the zone initialize state0 command to set the initial state of all elements to zero.

[0280] S307 defines the FISH function: The FISH function `disp_average` calculates the average displacement of a specified list of grid points; the FISH function `disp_closure` calculates the displacement closure value of two lists of grid points, used to monitor deformation during tunnel excavation; the FISH command defines global grid point pointers `gplist1`, `gplist2`, `gplist3`, and `gplist4`, pointing to grid points at critical locations in the tunnel; and the FISH function `v_closure` calculates the displacement closure values ​​in the vertical and horizontal directions and records historical data.

[0281] S308 Excavation Relaxation: Define the excavation zone and set excavation parameters using the command `zone relax excavate name 'Excavation' minimum 0.05step 10000 range group 'Excavation'` to simulate the step-by-step excavation process of the tunnel; solve the model using the command `model solve cycles 10001` to simulate the mechanical response during the excavation process.

[0282] S309 Material Property Update: The material model of the excavation area is set to null using the command zone cmodel assign null range group 'Excavation', indicating that the area has been excavated.

[0283] S310 final solution: The final solution is performed using the command "model solve cycle 20000" to ensure that the model reaches equilibrium in its mechanical state after excavation; the calculation results and state of the model are saved as the file "tunnel1" using the command "model save 'tunnel1'" for easy analysis and review later.

[0284] In summary, the rock mass engineering numerical analysis method based on the IMASS constitutive model of the present invention has the following advantages:

[0285] (1) The IMASS constitutive model can better describe the entire process of rock mass from integrity to fragmentation and then to expansion. It has significant advantages in simulating complex behaviors such as strain softening and expansion of rock mass. It can more realistically reflect the mechanical behavior of rock mass during excavation and improve the accuracy of tunnel stability analysis.

[0286] Specifically, this is achieved by embedding the IMASS constitutive relation into the numerical model and combining it with its built-in damage variables. The correlation mechanism between sloss and volume expansion is achieved. The IMASS model is based on the generalized Hoek-Brown intensity criterion and incorporates a geological intensity index (i.e., sloss). ), rock block strength ( The system dynamically updates cohesion, friction angle, and bulk modulus using damage evolution functions. Simultaneously, it monitors the displacement, strain, and state variables of key monitoring points in real time using the FISH function, capturing the entire process response of the rock mass from the elastic stage → peak strength → strain softening → residual strength → volume expansion, thereby significantly improving the simulation accuracy for nonlinear behaviors such as large deformation of surrounding rock and expansion of fracture zones.

[0287] (2) By accurately simulating the mechanical behavior of rock mass during excavation, a more reliable basis can be provided for support design, thereby reducing engineering risks and costs and optimizing the support design and construction process of tunnels.

[0288] Specifically, this was achieved by constructing a step-by-step numerical simulation process of "excavation-support coupling" and using the FISH function to extract key parameters such as the range of the plastic zone of the surrounding rock, maximum displacement, damage distribution, and stress on the support structure. In the simulation, tunnel excavation units were activated sequentially, and support components such as anchor bolts and shotcrete were applied after a specified step length. By analyzing the differences in the response of the surrounding rock under different support timings and parameters, the effectiveness of the support scheme was quantitatively evaluated. This provides data-driven decision support for the selection of support timing, configuration of support strength, and optimization of construction sequence in engineering practice, effectively avoiding over-support or under-support.

[0289] (3) Applying the IMASS model to the numerical analysis of tunnels provides a new tool for numerical analysis of geotechnical engineering, expands the application scope of the IMASS constitutive model, and has broad application prospects;

[0290] Specifically, this was achieved by systematically integrating the IMASS constitutive model into the 3D / 2D numerical modeling process for typical underground engineering scenarios such as deeply buried tunnels, high-stress hard rock, or jointed rock masses for the first time, and by developing a dedicated FISH post-processing module. This module can automatically calculate and output axial strain ( ), volumetric strain increment ( ), damage indicators ( ), equivalent cohesion ( ) and friction angle ( The spatiotemporal evolution cloud maps or time history curves of key mechanical parameters such as rock mass and tectonic parameters have been obtained, which has solved the limitations of traditional Mohr-Coulomb or Drucker-Prager models in characterizing the nonlinear softening and expansion behavior of rock masses. This provides a generalizable technical paradigm for the refined numerical analysis of complex rock mass engineering.

[0291] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the technical solutions of the present invention.

Claims

1. A numerical analysis method for rock mass engineering based on the IMASS constitutive model, characterized in that, Includes the following steps: Model establishment and parameter determination: Based on the geometric dimensions of the slope or tunnel and the physical and mechanical properties of the rock mass, a three-dimensional numerical model is established in the numerical simulation software, and the density of the rock mass, the GSI value in the Hoek-Brown criterion, the uniaxial compressive strength UCS, the material constant mi, and the original rock modulus parameter are determined. IMASS constitutive model calling and parameter setting: Call the IMASS constitutive model in the numerical simulation software and set the parameters of the IMASS constitutive model; Numerical analysis and result processing: Numerical simulation calculations are performed in numerical simulation software to analyze the stress, displacement, and plastic zone distribution of the rock mass during the excavation process. The strain softening characteristics of the IMASS constitutive model are used to capture the transformation process of the rock mass from peak strength to residual strength.

2. The numerical analysis method for rock mass engineering based on the IMASS constitutive model according to claim 1, characterized in that, The establishment of the three-dimensional numerical model includes the following steps: Importing the geometric model: Use the zone import command to import a pre-generated mesh file, defining the geometry and mesh generation of the slope or tunnel; Define zone groups: Use the zone group command to mark different zones in the model to distinguish between the rock mass and the excavation area; Generate outer surface mesh: Use the zone face skin command to generate the outer surface mesh of the model.

3. The numerical analysis method for rock mass engineering based on the IMASS constitutive model according to claim 1, characterized in that, The invocation and parameter settings of the IMASS constitutive model include: a) Invoking the IMASS constitutive model: Use the commands `model configure imass` and `zone cmodel assign imass` to configure the model and specify that the IMASS constitutive model should be used; b) Set IMASS model parameters: Assign the rock mass physical and mechanical parameters to the unit cells one by one using the zone property command, and activate IMASS’s unique peak-residual-limit three-stage strength evolution and volume expansion algorithm. The rock mass physical and mechanical parameters include intact modulus, geological strength index GSI, material constant mi, uniaxial compressive strength UCS, and weakening multi-criteria coefficient.

4. The numerical analysis method for rock mass engineering based on the IMASS constitutive model according to claim 1, characterized in that, The numerical simulation calculation includes the following steps: Apply boundary conditions: Use the zone face apply command to apply boundary conditions and fix the velocity of the model in each direction; Initialize in-situ stress: Define tunnel depth, maximum z-coordinate and gravitational acceleration, apply gravity, and initialize the initial stress of the rock mass; Reset displacement, velocity, and state: Use the zone gridpoint initialize and zone initialize state commands to set the initial displacement, velocity, and state of all grid points to zero; Define FISH functions: Write functions using the FISH language to calculate and record axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus parameters; Excavation relaxation: Use the zone relax excavate command to define the excavation area and set the excavation parameters to simulate the step-by-step excavation process of the tunnel; Solve the model: Solve the model using the model solve command to simulate the mechanical response of the rock mass during the excavation process; Save model state: Use the model save command to save the model's calculation results and state to a file.

5. The numerical analysis method for rock mass engineering based on the IMASS constitutive model according to claim 1, characterized in that, The IMASS constitutive model includes a rock mass strength peak envelope and two softening yield envelopes. The definition formula for the rock mass strength peak envelope is: ， ， ， ； The defining formulas for the two softening yield envelopes are: ， in, It is shear strength. It is normal stress. Equivalent roughness, It is the strength of the rock block, and It is the basic angle of friction of the rock block; ， It's porosity. It is the rounding exponent, where For partially rounded / smooth blocks, For angular / rough blocks, and Applicable to very sharp, angular / very rough blocks, when shear strength is converted into a strength envelope. The space is approximated by the Hoek-Brown envelope with the following parameters: ， ， ， Maximum porosity is 40%. The default value is 30°.

6. The numerical analysis method for rock mass engineering based on the IMASS constitutive model according to claim 1, characterized in that, The calculation formulas for parameters such as axial strain, damage index, volumetric strain increment, cohesion, friction angle, density, and modulus are as follows: Axial strain : ， in, To monitor the displacement of the point in the Z direction, () represents the initial height of the sample or rock mass; Damage indicators : ， in, This is the first principal stress; It is the third principal stress; It is the peak first principal stress; Alternatively, it can be directly defined by internal state variables of IMASS, characterizing the degree of softening from peak intensity to residual intensity, with a value range of [value range missing]. ; Volumetric strain increment : ， in, For the strain increments in each principal direction; Cohesion With friction angle : Based on the generalized Hoek-Brown strength criterion and damage state evolution: ， in, , , , Cohesion With friction angle The equivalent of obtaining the tangents of the Mohr-Coulomb envelope and the Hoek-Brown envelope under the current stress state is as follows: ， ， density : When considering the volume expansion effect, the density is updated as a function of porosity: ， in, For the initial density, and These are the initial volume and the current volume, respectively. Tangent modulus : Based on geological intensity indicators by the IMASS model intact rock modulus and damage status evolution: ， Among them, the degenerate function It can be represented as: , ( Take 10~15).

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